The present invention generally relates to intravascular balloon catheters, and more particularly, to a flow regulator valve for regulating the flow of inflation fluid being delivered to a stent delivery balloon catheter.
Angioplasty is a procedure where a balloon is positioned in an artery at the site of a lesion and expanded in order to compress the lesion and enlarge the restricted area in the artery. In this procedure, a balloon is formed on one end of a catheter. The catheter is inserted transluminally to maneuver the balloon through the patient""s vasculature to the site of the lesion. When the uninflated balloon is properly positioned at the lesion, the balloon is inflated to dilate the restricted area.
In these procedures there may be restenosis, also referred to as recurrent stenosis, of the artery. Restenosis may require another angioplasty procedure, a surgical bypass operation, or some method of repairing or strengthening the area. To reduce the risk of restenosis and strengthen the area, a physician can implant an intravascular prosthesis for maintaining vascular patency, typically called a stent.
A stent is a device used to hold tissue in place or to provide support for a graft or tissue joined while healing is taking place. Stents are typically implanted by use of a catheter which is inserted at an easily accessible location and then advanced through the vasculature to the deployment site. The stent is initially maintained in a radially compressed or collapsed state to enable it to be maneuvered through a body lumen. Once in position, the stent is usually deployed either automatically by the removal of a restraint, or actively by the inflation of a balloon about which the stent is carried on the deployment catheter.
In reference to balloon catheter stents, a variety of devices are known in the art for use as stents, including coiled wires and wire mesh sleeves in a variety of patterns that are configured to be crimped onto a balloon catheter. Typically, the stent is mounted on and crimped to the balloon portion of the catheter. The catheter is introduced transluminally with the stent mounted on the balloon. The balloon is then inflated to expand the stent to a larger diameter to implant it in the artery at the lesion. An optimal clinical outcome requires correct sizing and deployment of the stent. An under deployed stent will have struts that are not in good apposition with the arterial wall.
Struts of the stent which are not properly deployed can create disturbed blood flow, stagnant regions of flow, and consequently create a high risk of thrombosis. Not being pressed into the arterial wall, they are unlikely to be endothelialized. This creates a long-term risk of thrombosis. Overexpanded stents produce over sizing or over expansion and consequent damage to the arterial wall.
The damage can span a range from simple penetration of the intima to tearing of the IEL (inner elastic lamina), media EEL (outer elastic lamina), and adventitia. Damage of the vessel wall has been shown to stimulate an inflammatory response that is linked to greater neointimal proliferation. Consequently, excessive vessel damage is believed to be a factor for the presence and degree of instent restenosis.
A common theme in PTCA (Percutaneous Transluminal Coronary Angioplasty), with or without stenting, is that a bigger lumen is better. However, this concept is tempered by the fact that vessel damage must be avoided. Certainly, the two biggest complications of stents, namely, restenosis and SAT (subacute thrombosis), are directly affected by the accuracy of stent deployment.
Another important aspect of stent deployment is the rapidity with which the stent is expanded. For balloon deployed stents, this is controlled by balloon inflation. Inflation is usually achieved through manual inflation-deflation devices (indeflators) or a xe2x80x9csmartxe2x80x9d indeflator unit that possesses some automation. In general, slower inflation is better. During inflation, kinetic effects create non-equilibrium conditions. For example, the friction of the balloon against the stent is affected by inflation rate. The stents, being made of metal also, have elastic versus plastic deformation behavior. A fast inflation/deflation cycle can result in higher levels of stent recoil. Inflation speed affects the uniformity of stent deployment along its length. Often, the distal and proximal ends of the balloon inflate first. A dumbell or dog bone shape is created which exerts a net inward force on the stent. Consequently, fast stent inflation may lead to more stent shortening. Ideally, the stent is deployed uniformly, with an even spreading of the struts around the periphery. Fast deployment is believed to increase the likelihood of struts being clustered together in sections and overexpanded in others.
In addition to the deployment problems listed above, areas where the stent is overexpanded have an increased chance of plaque prolapse. There are many potential reasons why inflation speed affects stent expansion. Catheter balloons can be folded in a non-uniform way. Balloon folds can get stuck or xe2x80x9ccaughtxe2x80x9d on stent struts. The lesion environment is rarely uniform, or with a perfectly concentric plaque. Lesions are typically eccentric, sometimes with fibrous or calcified focal regions. Consequently, the resistance to radial expansion of the balloon may be greater in certain directions resulting in an eccentric deployment. Lastly, in clinical practice, the process of stent implantation can become routine. Such familiarity often leads to shorter procedural times which tend to beneficial for the patient except for steps, such as stent inflation, where faster is not always better.
An improved intravascular stent delivery device is therefore needed to overcome the problems in the prior art. More particularly, the improved stent delivery device must provide a higher degree of safety than conventional delivery devices and must be comparatively inexpensive to manufacture. The present invention satisfies these and other needs.
Briefly, and in general terms, the present invention provides a new and improved apparatus and method to be used with balloon catheters. More specifically, the apparatus and accompanying method provide a flow regulator for regulating flow of an inflation fluid to a stent delivery balloon catheter.
In general terms, this invention is characterized by a valve regulator in fluid communication with the expandable portion, usually a balloon, of an inflatable balloon catheter. Situated in the flow path of the inflation lumen, the valve regulates the flow of liquid used to inflate the balloon. The valve is constructed to restrict flow and to respond to pressure applied to assure a desired inflation rate. On deflation, the valve offers little or no resistance, allowing the balloon to be deflated quickly. The present invention can be particularly useful when used with a stent delivery catheter to achieve uniform expansion of the stent at a desire inflation rate.
In one aspect of the present invention, the regulator incorporates a body having on its distal end a connector for connection to the balloon and on its proximal end a connector defining a control chamber for connection with an inflator. The chamber is configured at the distal end of the device with an orifice. A restrictor in the chamber is operable in response to the fluid flowed distally toward an orifice to cooperate with the orifice to form a predetermined flow area for flow therethrough at a certain flow rate. When fluid is flowed in the proximal direction through the chamber, the restrictor moves away from the orifice to forming a second flow area larger than the first flow area for flow in the opposite direction and at a greater flow rate.
The restrictor can include a poppet carried floatably in the chamber and shiftable from one end to the other to engage respective proximal and distal stops. The poppet may be round and perforated to provide for flow therethrough at a controlled rate. The poppet may be compressible so that, upon application of high pressure, it will expand laterally to reduce the flow area therearound to reduce the flow rate. Travel of the poppet in the opposite direction may be limited by contact with the axial ends of radial fins arranged in a radial array.
The present invention also contemplates a method of implanting an expandable intra-luminal stent. First, the stent is delivered by an inflatable delivery balloon incorporating a flow control valve. The valve is of the type limiting flow of a selected inflation fluid in one direction toward such balloon. In this fluid flow direction, the flow rate is controlled so as to expand the stent at a selected rate. When the fluid is flowed in the opposite direction, the rate is much greater so as to quickly deflate the balloon. Additionally, it is possible to control the fluid flow in one direction by reducing the flow rate in response to increased fluid pressure.
This invention may be employed to control the expansion, via an inflation balloon, of any endoluminal stent. The stent can be intended for the coronary, iliac, carotid, neurological, renal, or other peripheral vasculature. There are no restrictions on the type of stent, size, or its placement. The present invention can be a separate device which can be attached to an inflation device and the balloon catheter, or it can be built directly into, for example, the proximal hub of the catheter. The present invention also can be build directly into the inflation device, if desired.
These and other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the features of the invention.